J. Nannoplankton Res. 28 (2) , 2006, pp .85-87 © 2006 International Nannoplankton Association85

ISSN 1210-8049 Printed by Cambridge University Press, UK

Use of a microdrill for high stratigraphical resolution
calcareous nannofossil analysis, and a modified filtration
methodAllan Gil S. Fernando*, Hisatake Okada, Hiroshi Nishi, Reishi
Takashima
Division of Earth and Planetary Sciences, Graduate School of Science , Hokkaido University, NlO W8 Sapporo 060-0810, Japan; *braarudosphaera@yahoo.com
Manuscript received 4th November, 2005; revised manuscript accepted 22nd May, 2006Abstract A tool capable of obtaining sediment samples at ~lmm intervals is introduced in this short paper. The
microdrill , as the tool is called, was developed in preparation for a high-resolution calcareous nannofossil analysis
of Cretaceous black shale sequences .
Keywords Microdrill, high-resolution analysis, calcareous nannofossils, Cretaceous, black shales
1. Introduction
Obtaining sediments for calcareous nannofossil analysis
has never been a real problem, since only a very small
amount of sediment is needed for any type of qualitativeor quantitative nannofossil study. In an attempt to study
nannofossil distributions through intervals at high resolution , however, obtaining adequate amounts of sample
material becomes a serious problem, especially when coupled with limited amounts of available sample, for example from Ocean Drilling Program (ODP) cores. To
address this problem, and in preparation for the quantitative analysis and characterisation of nannofossil assemblages between laminated and non-laminated black shaleintervals from the Vocontian Basin of SE France, we conceptualised and developed a tool capable of obtaining
samples at ~lmm intervals. The microdrill, as the tool iscalled, can be equipped with drill-bits of 0.1 to l.Omm indiameter (Figure 1).

2. Methodology
2.1 Microdrilling
A sample is placed on the stage/platform and is fixed by aclamp (Figure la). The sample should preferably have aplanar surface so that the waxed paper (~12cm2), uponwhich the powdered sample is to be collected, can be easily attached. If the sample does not have a flat surface ,some of the sediment powder produced from the drilling
will go into the space between the waxed paper and thesample. A circular hole (~6mm in diameter) is made in thewaxed paper with a hole-puncher. The hole is covered
with adhesive tape (magic tape is recommended), and ,with the sticky side facing the sample, attached to the surface of the sample/core prior to drilling (Figure lf). Thehole should be centred on the area of interest, where thedrilling will take place. The use of waxed paper prevents
contamination with previously drilled holes by keeping
the powdered sample out of contact with the sample surface. The adhesive tape, on the other hand , ensures effi-

cient recovery of the powdered sample by keeping thearea around the drill-hole fixed, enabling the powderedsample to be collected above the waxed paper during
drilling. After each hole is drilled , the contents of thewaxed paper are transferred to another piece of waxed
paper, where it is weighed (for the filter method, discussed below) or collected to make smear-slides. Since
multiple drillings are sometimes necessary per level, several holes can be made in the waxed paper so it can beused again after transferring each sample. The risk of contamination is further avoided by cleaning the surface ofthe sample with an air-duster after each sample is taken
and cleaning the drill bits ultrasonically after each use.
The microdrill (manufactured by Minitor CompanyLtd., Japan) is equipped with a digital ruler to ensure that
holes are drilled at the same level , in the case where multiple drillings are necessary per level, and that the intervals between samples are regular (Figure ld). The diame. ter of the drill , the number of holes per level, and theamount of sample required ultimately depends on how
much sample is available , and on the purpose of the study.
Experimental holes drilled in several samples (limestonesand black shales) have shown that the amount of sedimentpowder produced is proportional to the drill-bit diameter.
The average amount of sediment produced per holeranges from 0 .9-2.4mg (0.8mm drill) to 4.2mg (l.Ommdrill).
In our study, the 0.8mm drill was chosen so as to beable to obtain samples at lmm intervals with negligible
overlap between successive samples. Two to three holes
were made per interval, with enough sediment produced(2.7-4.5mg) to make slides for biostratigraphic and semiquantitative palaeoenvironmental nannofossil analyses(smear-slide method of, e.g., Bown & Young, 1998).
Although counted data from smear-slides are considered
to be semiquantitative , results from this type of analysis
have been found to be comparable with quantitative
results obtained from a filtering technique (Backman &86

Fernando, Okada. Nishi, Takashima

Shackleton, 1983). Currently available quantitative methods (i .e ., Andruleit, 1996; Flores & Sierro, 1997; Geisenet al., 1999; Okada, 2000) require greater amounts of sediment, which even the microdrill method would have difficulty providing, especially with limited sample material
available. In such cases, smear-slide analysis is the usual
option via which to collect data, either as relative abundance values or, as Backman & Shackleton (1983) havesuggested, as a measure/approximation of nannofossil
abundance (no. coccoliths/mm2).

age from the technique. Initial investigation of smearslides prepared from the powdered samples has shown
moderately- to well-preserved nannofossils. We believethat etching observed in some of the specimens is due topoor preservation within the black shale intervals rather
than mechanical breakage during drilling. This is supported by scanning electron microscopy of several sections
from the core (F. Giraud , pers. comm., 2005). A modified
filtering technique (Okada, 2000) is suggested to take into
consideration the small sample size and to eliminate theproblem of size fractionation.

2.2 Filtration
One problem which is usually associated with smearslides , however, especially if not done properly, is the tendency oflarge forms (such as nannoconids) to concentrateor be more common in areas with thick sediment smear
and/or along the slide edges. To minimise this problem insize fractionation, we employed a filtering technique(Okada, 2000), modified to suit our study. This techniqueallows us to make quantitative analysis of calcareous nannofossil assemblages even with a small amount of sediment. The method is outlined below.
The sediment powder produced from drilling isweighed. One to 1.5mg of sediment is suggested to avoid
crowding the filter. The weighed sample is placed in a test
tube, mixed with lOml of buffered, distilled water, agitated in an ultrasonicator for~ 10 seconds, and homogenised
against a tube-mixer for several seconds. After homogenisation, the contents of the test -tube are poured into a small
beaker containing 150-200ml of buffered, distilled water.
The contents of the beaker are then filtered through a
0.45Jlm Millipore filter. The filter can either be air- oroven-dried. Okada (2000) suggested drying the filter in anoven for 10-30 minutes at a temperature of so·c. Afterdrying the filter, a portion (~ 1.2cm2) is cut out, placed ona glass slide , rendered transparent with a drop of immersion oil and covered with a coverslip whose edges are
fixed with nail polish. To obtain nannofossil abundance
data (number of coccoliths/g of sediment), the total number of specimens counted, and observed fields of view(FOV) are recorded , so that:

Acknowledgements
This article is part of the study of calcareous nannofossils fromthe black shale sequences of SE France and is supported by the21 st Century COE Program'The Neoscience of Natural History'of Hokkaido University. The authors thank Drs Jackie Lees andJens Herrle for their helpful suggestions and reviews of the initial draft.

References
Andruleit, H. 1996. A filtration technique for quantitative studies of coccoliths. Micropaleontology, 42(4): 403-406.
Backman, J. & Shackleton, N.J. 1983 . Quantitative biochronology of Pliocene and early Pleistocene calcareous nannofossils from the Atlantic , Indian and Pacific Oceans. Marine
Micropaleontology, 8: 141-170.
Bown, P.R. & Young, J.R. 1998. Techniques. In: P.R. Bown(Ed.). Calcareous Nannofossil Biostratigraphy . British
Micropalaeontological Society Series. Chapman &Hall/Kluwer Academic Press, London : 16-28.
Flares , J.A. & Sierra , F.J . 1997. Revised technique for calculation of calcareous nannofossil accumulation rates.
Micropaleontology , 43(3): 321-324.
Geisen, M ., Bollmann, J., Herrle, J.O ., Mutterlose, J. & Young ,J.R . 1999. Calibration of the random settling technique forcalculation of absolute abundances of calcareous nannoplankton. Micropaleontology , 45(4): 437-442.
Okada, H. 2000 . An improved filtering technique for calculationof calcareous nannofossil accumulation rates . Journal ofNannoplankton Research , 22(3): 203-204 .

nannofossil abundance = (specimens counted) x (area of filtered portion [mm2]) x (g-1 of sediment used)#FOV (area of FOV in mm2)

Aside from the number of coccoliths per unit weightof sediment, which can be calculated from the formula
given above, the data obtained can also be reported as relative abundance values and number of nannofossils perunit area , following the suggestion of Backman &Shackleton (1983) .

3. Conclusions
The described methodology makes it possible to obtainhigh-resolution samples from consolidated materials. The
method, at present, is applicable only to calcareous nannofossils , since other microfossils (i.e., foraminifera andradiolarians) are large enough to suffer considerable dam-Use of a microdrill

87
MITCRODruLLEQ~MENTANDPARTS

c0.8- 0.9 mm drill bitsacore sample

Figure 1: a) Microdril1 equi pment set-up and parts. The sample is placed on the tage/platform and is fixed by a clamp. b) Drill apparatus. Verticalarrow indicate the aperture where the drill-bit , (c) , are inserted , while horizontal arrow indicates tbe position of the lock to keep the drill-bits inplace. Depending on the purpose of the study and amount of sediment needed, drill-bits with diameters of 0.1 to l .Omm can be used. d) One of two
digital rulers attached to the microdrill (top view). The digital rulers indicate the position of the drill -bits and are capable of measuring lateral andvertical movements (with re pect to the core/sample) at 0 .0 I mm intervals . e) Power-source and rotation speed and direction controller. Horizontal
arrow indicate the rotation speed controller. 0 Drilling set-up as described in the methodology section